A typical cell of a wireless telecommunications network has a central base station transmitting and receiving radio frequency (rf) signals over a geographical area or cell bounded by a boundary of theoretical equal signal strength with adjacent cells. The network is made up of a plurality of such cells mosaiced over a wider geographical area, as is well known in the art. The cell may be divided into sectors with typically one or more single beam antenna of the base station covering each sector.
There is currently a requirement from end users of mobile user equipments for location aware services, in which the network is aware of the location of the end user. An example might be services for advising end users of traffic jams in their location or for advising end users of local services, such as restaurants in their location.
Several schemes have so far been utilised to determine position location of a user equipment within a telecommunications network. Cell ID and enhanced cell ID provide position location by identification of the cell within which the end user equipment is located. While this system requires no modifications to the user equipment, it cannot provide precise location positioning. Another alternative, Global Positioning System (GPS) is relatively expensive, although accurate. It suffers from the disadvantage that it can take some time for a user equipment to acquire and lock on to satellites, coverage is poor indoors, power consumption by the user equipment is high and a specially modified user equipment is required. Assisted GPS enables the user equipment to acquire and lock on to a satellite more quickly but still suffers from the other disadvantages of GPS. Enhanced-Observed Time Difference (E-OTD) provides relatively accurate position location, but again requires modified user equipments. In addition network wide synchronisation or additional timing measurement devices have to be deployed in the network. Finally, Cumulative Virtual Blanking (CVB) is a complex scheme which enables the deployment of E-OTD in Code Division Multiple Access (CDMA) networks. Again modified user equipments are required.
User equipment position location can be derived by triangulation between multiple base stations. However, this requires an array of antennas in each sector of each base station in the network. Algorithms which act directly on the outputs of the antennas (or antenna columns) of such an array are expensive to implement. This is because they require either a full receiver chain at each output, or a single receiver chain plus a complex and high speed switching module to commutate this single receiver across multiple antennas.
To maximise the capacity of the base station downlink, it has been proposed to use multi-beam or beamformed antenna arrays to cover each sector of the cell of the base station, for example, three beam per sector deep cusp antennas. It is envisaged that the additional equipment complexity of the multi-beam antenna arrays and associated signal processing will be compensated for by the enhanced downlink capacity achieved. The angular position of a user equipment within a cell sector is most likely to be aligned in some way with the beam through which the received signal power is the greatest however, estimating the Angle of Arrival (AoA) of a signal on the uplink simply by picking the beam with the strongest signal would not be accurate enough for practical purposes because in the three beam per sector case, with deep cusp beams, each beam has a width between crossovers of around 40°.